Move Spaceship Earth!

David A. Wheeler

2010-12-23 (revised 2014-01-27)

In the really long term, the prognosis for life on Earth is bleak.
Over the next few billion years, the Sun will get larger and brighter,
eventually becoming a red giant
with a size similar to Earth’s current orbit.
A
1993 paper
suggested that because the Sun will lose mass over time,
the Earth will move away and escape being gobbled up by the sun.
Unfortunately, a more recent paper
(“Distant future of the Sun and Earth revisited”, 2008)
determined that, due to tidal interaction and drag, the Earth
won’t escape.

Bummer.

But never mind that; the real problem
is that the Earth will eventually
be too hot for liquid water to exist on its surface... which would be
the end of life based on water.
The 2008 paper estimated that this would happen
within approximately one billion years.
A
more recent 2013 paper by Wolf and Toon analyzed the process in much more detail
(summarized here).
Wolf and Toon found that the Earth has more time, once
Earth's complex weather processes are examined in much greater detail:
"Earth's climate may remain safe against both water loss and thermal
runaway limits for at least another 1.5 billion years and probably for
much longer."
However, the final outcome is not in doubt.
Basically, we’re toast.

So instead, let’s plan on moving the Earth
if we’re still around.
We don’t have the technology today, but a billion years is a long time.
In just 10,000 years we’ve gone from hunting & gathering
to Android cell phones.
A billion years is 100,000 units of 10,000 years — a very big number.
I think it is reasonable to expect that our descendants will work out
better technology than we have, given all that time,
including far superior methods to create and control energy.
The big problem with today’s spaceship Earth is that it lacks a steering
wheel... so, let’s create one.

Now, it’s very possible that our descendants will be able to work out
game-changing radical new technology.
For example, maybe they could create a wormhole that simply repositions
the Earth to any location that they wish.
But if they simply have far better methods to create and control energy,
what could they do?

It turns out the answer is, “quite a lot”.
Now, you can’t put a lasso around the Earth, obviously;
it’s spinning and you don’t want to stop that.
And you don’t want to put a megarocket on the Earth to move it; that
would heat Earth’s atmosphere in unpleasant ways.
But you could put a big rock nearby and attract it gravitationally.
Indeed, this is one of the ways that have been proposed for moving asteroids.

So, do we have any big rocks available?
The answer is, sure.
There are lots of asteroids we could use for the purpose strewn about
the solar system.
We also have a big rock close by, ready for use —
we usually call it “the Moon”.
Just attach some big honkin’ propulsion system to some
rock (such as an asteroid or the Moon), move it
into the right place (in the direction where you want the Earth to go),
and you could slowly perturb
the Earth’s orbit to something more favorable.
This is something you want to do slowly, else tidal effects will be
disastrous.
You’d also have to be careful;
you don’t want to significantly change
the Earth’s rotation speed or the angle of its axis of rotation
(though compared to getting broiled by the Sun, perhaps that’s
a trade-off you could live with).
Also, you’d better make sure the propulsion system is reliable;
having the Moon or other big rock crash into the Earth could ruin your day.
Although I focus on the Moon here, it appears that an asteroid would do;
Can Life on Earth Escape the Swelling Sun? notes that
“One team at Santa Cruz University in California has proposed
capturing a passing asteroid and using its gravitational effects
to "nudge" Earth's orbit outward. A continuous asteroid passage
every 6,000 years or so could keep Earth at a comfortable distance
and give life another 5 billion years on the planet.”

A propulsion system that directly pushed the Moon or other
large object away from the Earth
might throw matter or energy directly toward the Earth, if done naively,
and that might be unpleasant.
One partial solution might be to use several outputs, each of which were
angled away but when combined pointed in the right direction.
That would help with steering, too, by varying the amount of thrust
from each.

One alternative to using gravity would be electromagnetism —
create a big electromagnet, and turn it on when you want to pull (or push).
Turning it on would take more energy, but it would mean that you get to
decide when it’s on.
It would be complicated if the Earth’s magnetic pole was not near
its axis of rotation, though, and you would probably need to pull it
roughly in its direction of rotation.
Otherwise you might completely change the
Earth’s spin, with annoying consequences for anyone on it.
You also need to make sure which direction is magnetic north, and which
is magnetic south, since that occasionally switches.

So now that we’re moving the Earth, where should we put it?
The short answer is that the best place varies over time.
As the Sun changes, you want to move it to some zone that is habitable.
Here are some possibilities in the first few billion years to come:

Put it closer to Mars’ orbit, but not in it.
If you get the orbits of Earth and Mars too close together
you might need to work out a resonance (so that they
don’t interfere with each other).

Put it in Mars’ orbit, but on the other side of the Sun.
That might be inconvenient if you wanted to go back and forth
between Mars and Earth often, but if you can move a planet, that might
not really be inconvenient.

Put it in a significantly different inclination from Mars (and most of the
rest of the Solar system). This works, especially if you put the Earth
in resonance with Mars’ orbit. The same thing happens with Pluto and
Neptune; sometimes Pluto is closer to the Sun than Neptune,
yet Pluto and Neptune won’t collide.

Move Earth out, and move Mars too.
Mars does not have a significant magnetic field, so electromagnets are
probably not the answer for moving Mars (unless we tinker with Mars).
Mars’ atmosphere is not much today, but by that time
it’ll probably be colonized and have more atmosphere, so most
propulsion systems placed directly on Mars will be undesirable too.
Gravity would work, of course...
but what do you use to attract Mars elsewhere?
You could use our Moon to also move Mars, but our Moon is very helpful for
keeping Earth’s axis stable,
and moving the Moon back and forth would be painful.
The moons of Mars, Phobos and Deimos, are very small, so
they wouldn’t be great for moving them (though with enough time they
might help).
The good news is that the asteroid belt contains
Ceres — the largest body in the asteroid belt.
Ceres’ mass is so large that its own gravity pulls it into a spherical
shape.
We could move Ceres to Mars, and use Ceres to pull Mars somewhere else.
If we moved Mars too far out it’d end up in the asteroid belt;
that process would probably mean that Mars would
get a lot of rocks landing on it until things settled.
But it would be possible.

The Sun will continue to change, so moving the Earth to keep it
habitable will not be a one-time event; the 2008 paper has the details
of what the Sun will do.
In about 5.2 billion years from now, the Sun will be at the end of
its “main sequence”, at which point the Earth will need to be between
1.29 to 1.86 AU distant from the Sun (a range that includes Mars’
current orbit).
Then the Sun’s core will run out of hydrogen;
hydrogen will begin to burned in a shell instead, and the
Sun will begin climbing up the red giant branch (RGB) curve, becoming
much bigger and brighter than today.
By about 7.6 billion years from now, the zone where liquid water can
exist on a planet’s surface will have shifted to 49.4-71.4 AU.
That means that by that time
we need to move Earth beyond Pluto’s current orbit
(Pluto’s maximum distance from the Sun is 49.3 AU).

As the Sun continues to age it will experience tremors and other nastiness.
Rather than moving the Earth closer for heat and light (and experiencing
those ill effects),
we’d probably need to keep it far away from the Sun and
give it an alternative heat and light source.
This alternative source could either on the moon or elsewhere;
perhaps Jupiter could be moved and lit as a small star for our benefit.
Eventually, though, the Sun will become a slowly-cooling white dwarf.
At that point, what should we do for energy?

So, authors need to stop saying stuff like
“the Earth will be destroyed in X billion years”.
That might happen, but only if no one intervenes.
Rescuing home planets isn't even a new idea;
E.E. “Doc” Smith's 1948 science fiction classic Triplanetary
notes, in its third paragraph,
that “the Arisians... had to work against time in
solving the engineering problems associated with moving a planet from
an older to a younger sun”.

We absolutely do not have the technology to do this today;
we have nothing even close.
But people 10,000 years ago didn’t have computers, either.

But it turns out that there are things we can do today
that relate to this idea:

Take care of the Earth we have; we might use it for a while.

Fund science, especially fundamental physics.

Fund the development of technologies to generate and harness energy.

Indeed, even in the short term, techologies to develop low-cost and
high-yield energy without depending on oil
would eliminate a vast number of problems that
we (the current crop of humans) have to deal with today.
And who knows, some of this might help us move to better real estate in
the future.